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Monday, 13 February 2012

Carotenoids
are compounds constituted by eight isoprenoid units (ip). The ip units are
joined in a head-to-tail pattern, but the order is inverted at the molecule center
(Delgaldo and Lopez, 2003).Carotenoids
are naturally occurring tetraterpene pigments widely distributed through out
the living world (Zdzlaslaw, 2002). Lycopene (C40 H56) is
considered the first colored carotenoid in the biosynthesis of many other natural
carotenoids and it has a linear structure (Delgaldo and
Lopez, 2003). Lycopene is the carotenoid that gives the red color to tomatoes
and watermelons.
Moreover, it is also common to find acyclic, cyclic, and shortened carotenoids,
among others. Carotenoids have very important
biological activities and their use as food and feed today is recommended
largely due to their vitamin A and antioxidant activities important in
maintaining life
(Delgaldo and Lopez, 2003; Zdzislaw, 2002). Due to their ability to quench singlet oxygen and trap peroxyl
radicals, carotenoids have been described as excellent antioxidants. In
addition, an inverse association between the ingestion of carotenoid-containing
fruits and vegetables and the risk of certain forms of chronic diseases has
been suggested (Østerlie and Lerfall, 2005).Carotenoids
of the higher plants are found in roots, stems, leaves, flowers and fruits
giving them the red, yellow, and orange colors. In higher plants, carotenoids
are found in plastids (Delgaldo and Lopez, 2003). They are in the chloroplast
of photosynthetic tissues and they are found in chromoplasts. The majority of
the carotenoids found in plant tissues is β-carotene (Zdzislaw, 2002). Zdzislaw (2002) defines β-carotene as an
asymmetrical molecule of 40 carbon atoms, consisting of 8 isoprene units having
11 conjugated double bonds and 2 β-ionone rings.Animals derive
carotenoid pigments by consumption of carotenoid-containing plant materials.
The name carotenoid has been derived from the major pigment of the carrot (Zdzislaw, 2002).

The color of carotenoid pigments is as
a result of the presence of a system of conjugated double bonds. A minimum of
seven conjugated double bonds is required for the yellow color to appear. The
increase of double bonds results into a shift of the major adsorption bands to
the longer wavelengths, and the hue of carotenoids become more red (Zdzislaw, 2002). Because of the
highly conjugated double-bond system, carotenoids show ultraviolet and visible
absorption spectrum characteristics. According to Zdzislaw (2002), for most carotenoids, three peaks or two peaks
and a shoulder, are absorbed in the range of 400–500 nm. The absorption maxima
and molecular extinction values are significantly affected by the solvent used.

In unprocessed plants, usually all-trans double-bond configurations
occur, but cis isomers of each
carotenoid are also possible. Processing and storage cause isomerization of
carotenoids in foods and affect the color. The deepest color is due to
compounds with all-trans configurations.
So, increasing the number of cis bonds
results into gradual lightening of the color. This is because cis isomers absorb less strongly than
the all-trans isomer, and peak
at 330–340 nm (Zdzislaw, 2002).

Due to the presence of asymmetric
carbon atoms, many carotenoids have chiral centers. However, natural
carotenoids exist only in one of the possible enantiomeric forms, because the
biosynthesis is enantiomere selective.

Tomatoes have a high content of
carotenoids with lycopene being the main compound making up 80 to 90% of the
total carotenoid, followed by β-carotene (Delgado and
Lopez, 2003). The lycopene content in tomatoes increases with ripeness. New
tomato varieties with high and improved content have been developed and lycopene
products have begun to be commercialized (Zdzislaw, 2002). However, according to Delgado and Lopez (2003), other
modifications are required to use tomato extract as colorant because of its
strong flavor. Adding lycopene from natural sources to minced meat could lead
to a meat product with different taste, better color and with a well,
documented health benefit and a new functional food would be developed and may
be natural lycopene could replace nitrite added minced meat(Østerlie and
Lerfall, 2005).

Processing and stability

In processing or storage of colored
food, carotenoids are sensitive to treatments. High and short times are
preferred conditions during processing of carotenoid-containing foods ( Fennema
1996; DeMan, 1999; Delgado and
Lopez, 2003). Drying (uncontrolled)
leads to carotenoid degradation due to the presence of free radicals. In tomatoes,
the dehydration process leads to isomerization but it has been observed that
osmotic treatment does not affect the isomeric profile of lycopene (Delgado,
and Lopez, 2003). Freezing causes
little changes in carotene content. Blanching increases carotenoid content
relative to the raw tissue due to the inactivation of lipoxygenase which is
known to catalyze oxidative decomposition of carotenoids. Carotenoids are extremely
lipophilic compounds that are almost insoluble in water. In aqueous
surroundings they tend to form aggregates or adhere to surfaces (Zdzislaw, 2002; Fennema 1996; DeMan, 1999;Delgado
and Lopez, 2003)

Anthocyanins

Anthocyanins are flavonoids with a characteristic C6 C3C6
carbon skeletonmaking them the most commonly distributed
pigment group in plants kingdom (Deman, 1999; Fennema, 1996; Zdzislaw, 2002).

Anthocyanins occur in all higher
plants, mostly in flowers and fruits but also in leaves, stems, and roots. In
these parts they are found predominantly in outer cell layer and account for a
wide range of colors including blue, purple, pink, orange, red, magenta and
violet in the plant kingdom (http://www.food-info.net/uk/colour/anthocyanin.htm;
DeMan, 1999).
In food plants, the main sources of anthocyanins are berries, such as
blackberries, grapes, blueberries, and some vegetables, such as egg-plants (aubergine), red cabbage and avocado.
Other sources include oranges, elderberry, olives, red onion, fig, sweet
potato, mango, Hibiscus spp (musayi
plant) and purple corn. They play a definite role in attracting animals in
pollination and seed dispersal. Accordng to Zdzislaw (2002), they may also have
a role in the mechanism of plant resistance to insect attack.

The structure of anthocyanins is
based on a C15 skeleton consisting of a chromane ring bearing a
second aromatic ring. The cyclic structures are arranged in the pattern
C-6-C-3-C-6. Anthocyanins structure is complemented by one or more sugar
molecules bonded at different hydroxylated position of the basic structure (Delgado
and Lopez, 2003).

All anthocyanins are based on a single basic core structure, the
flavyllium ion (Zdzislaw, 2002).

Fig 8; Flavylium cation (Zdzislaw, 2002).

These side groups can be a hydrogen
atom (H), a hydroxide (OH) or a methoxy-group (OCH) depending on the considered
pigment. According to Zdzislaw (2002), from about 20 known naturally occurring
anthocyanidins, only 6 occur most frequently in plants and these include:
pelargonidin, cyanidin, peonidin, delphinidin, petunidin, and malvidin.

Classification

Anthocyanins are glycosides of polyhydroxy and polymetoxy
derivatives of 2-phenylbenzopyrylium or flavylium cation. They show high
diversity in nature but all are based on a reduced number of basic
anthocyanidin structure. Anthocyanin diversity is associated with the number of
sugars found in nature but glycosylated anthocyanins are formed with glucose,
rhamnose, xylose, galactose, arabinose, and fructose (Deman, 1999; Fennema,
1996; Zdzislaw, 2002).

The chemical combinations of these
sugars with organic acids to produce acylated anthocyanins also increase
diversity. Differences between individual anthocyanins are: the number of
hydroxyl groups in the molecule; the degree of methylation of the hydroxyl
groups; the nature, number, and position of glycosylation; and the nature and
number of aromatic or aliphatic acids attached to the glucosyl residue.

Substitution of the hydroxyl and
methoxyl groups affects the color of the anthocyanins. Color is also affected
by the number of hydroxyl and methoxyl groups. If more hydroxyl groups are
present, then the color goes towards bluish shade, and redness is increased if
more methoxyl groups are present (http://en.wikipedia.org/wiki/Anthocyanin;
Zdzislaw, 2002)

The anthocyanins constitute a large family of differently colored
compounds and occur in countless mixtures in practically all parts of higher
plants. They are of great economic importance as fruit pigments and thus are
used to color fruit juices, jams, wines, some beverages, canned fruit, fruit
syrups, yogurt, and other products. They are used as food additive with
European Union number E163.
In the USA, the grape color extracts were approved for use in non beverage
foods, where as grape skin extract (enocyanin) is permitted in beverages. (DeMan,
1999; Delgado and Lopez, 2003)

Processing and stability

Anthocyanins are water soluble strong colors and have been used to
color food since historical times (Delgado and Lopez 2003). Extracts of berries
have been used to color drinks, pastries and other foods. However, some
drawbacks in the use of anthocyanins as food colors exist.

Anthocyanins
are water soluble and pH dependent which restricts their use. For example the
color of red cabbage is enhanced with the addition of vinegar or other acid. On
the other hand, when cooked in aluminum pans which cause a more alkaline
environment, the color changes to purple and blue (http://www.food-info.net/uk/colour/anthocyanin.htm).

The color is
also susceptible towards temperature, oxygen, UV-light and different
co-factors. Temperatures destroy the flavylium ion, and thus cause loss of
color. Temperature also causes maillard reactions, in
which the sugar residues in the anthocyanins may be involved. Light may have a
similar effect (Delgado and Lopez 2003; Zdzislaw 2002). Oxygen may destroy the anthocyanins, as do other oxidizing
reagents, such as peroxides and vitamin C. Many other components in plants and
foods may interact with the anthocyanins either destroying, changing or
increasing the color. Quinones in apples for example, enhance the degradation
of anthocyanins whereas the addition of sugar to strawberries stabilizes the
color. (Delgado and Lopez, 2003; http://www.food-info.net/uk/colour/anthocyanin.htm)

All these factors limit the use of anthocyanins in foods. Some loss
of color during storage may be prevented by storing at low temperatures, in
dark containers or under oxygen-free packaging (Deman, 1999; Fennema, 1996;
Zdzislaw, 2002; Delgado and Lopez 2003).

In practice the
pure colors are very hard to obtain and most often (crude) extracts are used as
food colors. Grape peel (E163 (i)), and black currant extract (E163 (iii)) are
the most widely used anthocyanin mixtures in foods. (http://www.food-info.net/uk/colour/anthocyanin.htm)

Betalains

Betalains are immonium derivatives
of betalamic acid, with a general formula based on the protonated 1, 2, 4, 7,
7-pentasubstituted 1, 7- diazaheptamethin system (Delgado and Lopez, 2003). Betalains occur in centrospermae, mainly
in red beets, but also in some cactus fruits and mushrooms (Zdzislaw,
2002; Deman, 1996). Zdzislaw, (2002) reported
that they consist of red-violet betacyanins (λmax ~ 540 nm) and yellow
betaxanthins (λmax ~ 480 nm). The major betacyanin is betanin, glucoside of
betanidin, which accounts for 75–95% of the total pigments of beets. The other
red pigments are isobetanin (C-15 epimer of betanin), prebetanin, and
isoprebetanin. According to Deman (1996), the latter two are sulfate monoesters
of betanin and isobetanin, respectively. Unlike anthocyanins, betanins cannot
be hydrolyzed to aglycone by acid hydrolysis without degradation
(Zdzislaw, 2002).
The major yellow pigments are vulgaxanthin I and
II. High betalain content in beet root, on average 1% of the total solids,
makes this vegetable a valuable source of the food colorant (Deman,
1996; Zdzislaw, 2002).

Fig 9: Molecular structures of betanin
and isobetanin and the major yellow pigments, vulgaxanthin I and II (Zdzislaw, 2002).

Betalains
are found in different plant organs, and are accumulated in cell vacuoles,
mainly in epidermal and sub epidermal tissues (Delgado and Lopez, 2003). Some accumulate in plant
stalks such as in the roots of red beet.Betalains are also present
in the higher fungi Amanita, Hygrocybe, and Hygrosporus (Zdzislaw, 2002).

Classification:

Betalains are commonly classified
into two based on their structural characteristics;

(i)Betacyanins (red-purple)

(ii)Betaxanthins (yellow)

Each group of pigment is
characterized by specific R1-N-R2 moieties.R1 and R2 groups can be
hydrogen, aromatic group or another substituent. Betalain color is attributable
to the resonating double bonds. A large number of betaxanthins can be formed
with the same dihydropyridine moiety, by conjugation with several amine
compounds such as amino acids. The diversity of betacyanins is associated with
the combination of the basic structures (betanidin and isobetanidin) with
different glycosyl and acyl groups attached by the hydroxyl groups at positions
5 and 6. The most common glycosyl moiety is glucose and the most common acyl
groups are sulfuric, malonic, citric and caffeic acids.

Betalains as food color.

According to Delgado and Lopez
(2003), betalains have been in use as food colorants at least since the return
of the 20th century. Diaz et al., (2006)
reported that there is a growing propensity to substitute synthetic colorants
with natural pigments in the food industry. This is further confirmed by the
red beet betacyanins being approved for use as a food additive in the United
States of America (No. 1600), and in the European Union (E-162). Commercially,
the red beet betacyanins are exempt from batch certification (http://www.food-info.net/uk/colour).

Processing and stability

The most-studied betalains are found
in red beets (Beta vulgaris) in
which the main betacyanins are betanin and isobetanin (Delgado and Lopez,
2003). Betalains stability is affected by temperature, pH, oxygen, light, and
aqueous activity (Diaz et al., 2006).
According to Delgado and Lopez (2003), enzyme degradation is also an important
factor that must be considered when a betalain pigment product is to be
processed.

Zdzislaw (2000), reviewed that color
stability of betanin solution is strongly influenced by pH and heating.
Betanins are stable at pH values of 4–6, but thermostability is greatest between
pH values of 4 and 5. As a result of betanin degradation cyclo-DOPA and
betalamic acid are formed. This reaction is reversible.

Fig 10: Degradation of betanin (Zdzislaw, 2002)

Light and air have a degrading
effect on betanin according to Zdzislaw
(2002). These effects are cumulative, but some protection may be offered
by antioxidants such as ascorbic acid. Small amounts of metallic ions increase
the rate of betanin degradation. Therefore a chelating agent can stabilize the
color. Many protein systems present in food products also have some protective
effect (Zdzislaw, 2002).

Freeze-drying is the best method to
dry pigments which are sensitive to high temperatures (Diaz et al.,
2006).

On market, Beetroot red (E 162) is
available as liquid beetroot concentrate and as beetroot concentrate powders.
According to Zdzislaw(2002) and Delgado
and Lopez(2003), it is suitable
for products of relatively short shelf life, which do not undergo as severe
heat treatment such as meat and Soya protein products, ice cream, and gelatin
desserts.

Note that all
references used in all postings related to the topic of sausages, meat and meat
product colorings will be posted in the last article about this topic

About the authorMr.
Sempiri Geoffery, the author of this article graduated from
Makerere University witha Bsc In
Food Science and Technology Degree in January, 2011.

This is any substance that is added to food or
drink to change its color. (http://en.wikipedia.org/wiki/color).

Or

Food additive used to alter or improve the color of processed foods.
(http://encyclopedia.farlex.com/additive).
Food coloring is applied to
both commercial food production and domestic cooking. The
utilization of food colorants in foods is an important feature to the food
industry (i.e. to both manufacturers and consumers) (Muntean, 2005).

Reasons to use color additives

Consumers recognize color, flavor,
and texture as the main attributes of food with color being the most important
of the three (Delgado and Lopez 2003,http://en.wikipedia.org/wiki/color).
Today, food products are consumed far from where they
are produced. As a result, processing and transportation of food are necessary
to reduce degradation and loss of appearance. The use of color additives by the
food industry is thus necessary to restore the original food appearance i.e. the
added colorants, reinstate the novel look/color of foods after processing and
storage treatments where natural colorant content has been reduced; ensure
batch-to-batch color uniformity and masking natural variations in color; intensify
color normally found in food i.e. the addition of colorants enhances naturally occurring colors which are in low intensity to consumer expectations (Muntean, 2005); protect other
component e.g. flavors and
vitamins from damage by light (Zdzlaslaw, 2002); obtain the best food
appearance i.e. decorative or
artistic purposes such as cake icing (http://en.wikipedia.org/wiki/color);
preserve characteristics associated with food; help as
a visual characteristics of food quality i.e. it influences acceptability of
food, for example good quality fresh meat is expected to be bright red and any
deviation from that is viewed as spoilt (Deman, 1999); and also adds visual
delight and recognition/ identity to food products e.g. lime juice is expected to be green while
sausages are expected to be pink in color (Fennema, 1996).Therefore, addition of food colorants has become a regular practice
in the food industry to better or even alter the color of foods and drinks.

Food Colors/colorants used are
either synthetic (artificial), such as tartrazine and amaranth, made from
petrochemicals or natural colors such as chlorophyll, anthocyanins, caramel,
and carotene (Fennema, 1996).

Choice and application of
color

Color is a main quality parameter in
foods (in particular meats) to be commercialized (Cornforth, 1994). According
to Delgado and Lopez (2003), a number of factors must be considered when
selecting the better color additive for specific applications. These include;
color hue required, physical form (e.g. liquid, solid, emulsion), properties of
the food stuff that will be colored e.g. oily or water- based product, content
of tannins, pH and processing conditions (e.g. whether the process requires
heating or cooling, storage conditions). In addition to the above, one factor
of paramount importance is the relevant legislation (Zdzislaw, 2002).

Classification of colorants

Pigments can be classified in accordance with the different system.
These systems are clearly defined, but all are closely related (Zdzislaw, 2002); the same type of
colorants can be classified in different groups (e.g. carotenoids). Today,
classification of colorants by their origin and legislation are the most
important systems. This is in agreement with consumer preferences, which
clearly favor natural pigments over synthetic pigments obtained from laboratories
(Delgado and Lopez, 2003; Zdzislaw,
2002). Colors can be the natural ingredients of foodstuffs or other
natural ingredients that are not normally used, such as a foodstuff or as a
typical ingredient for a foodstuff.Also
considered as colors are products that are obtained by physical and/or chemical
extraction from foodstuffs and other natural ingredients whose coloring
ingredient has been extracted separately from nutritive and aromatic substances
(Zdzislaw, 2002).

According to Zdzislaw, 2002, dried and/or
concentrated ingredients or spices that are used in the production of
foodstuffs and have, in addition to aromatic, flavoring or nutritional
properties a secondary coloring effect, are not considered to be colors (for
example paprika, curcuma and saffron). If the use of an ingredient is based
exclusively on its coloring effect and it has no nutritional or aromatic
properties, it is then considered to be a color.

Systems of classification
of colorants.

According to Delgado and Lopez (2003), colorants are classified basing
on either;

Origin:

As synthetic colorants that are organic compounds obtained by
chemical synthesis e.g. Food Drug and Cosmetics (FD&C) colorants, natural
colorants that are organic compounds obtained from living organisms. According
to Østerlie and
Lerfall (2005),the
colorants are considered natural if they are from agricultural/biological
sources, extracted without chemical reaction and have been in use for a long
time e.g. carotenoids, anthocyanins, betalains and organic
colorants that are found in nature or obtained by synthesis e.g. TiO2.

The use of synthetic organic colors
has been recognized for many years as the most reliable and economical method
of restoring some of the food’s original shade to the processed product (Muntean, 2005). An
even more important application of synthetic colorants is to improve and standardize
the appearance of food products that have little or no natural color present,
such as dessert powders, table jellies, ice and sugar confectioneries. The
synthetic organic colors are superior to the natural pigments in tinctorial
power, range and brilliance of shade, stability, ease of application, and
cost-effectiveness (Muntean,
2005, Zdzislaw, 2002).

However, from a health and safety point
of view, they are less acceptable to consumers. Over the past years increasing
interest in natural food colorants has been observed (Zdzislaw, 2002).Synthetic food colorants are regulated by
the government with seven synthetic colorants currently approved for use in
food. These include 2 reds (#3 and
#40),2 blues (#1 and #2), 2
yellows (#5 and #6), 1 green (#3) (http://en.wikipedia.org/wiki/color). These
seven colorants are grouped by the color-giving chemical functional group they
contain. FD&C Red #40 and Yellow #6 both contain azo bonds (-N=N-) thus are
referred to as azo colorants. FD&C Blue #1, Green #3 and Red #3 belong to
the triphenylmethane group which contain three benzene rings attached to a
central carbon atom (Delgaldo and Lopez, 2003; http://en.wikipedia.org/wiki/color). Just as with any substance, the chemical structure of these
colorants determine its’ characteristics, for example if it is water soluble or
not. Water-soluble colorants are useful in water-based foods, but not in fatty
foods such as salad dressings and ice cream (Delgaldo and Lopez, 2003).

Natural Pigments

The naturally occurring colorants in
food plants are the customary sources of color in food although the added
colorants have assumed an extra vital role as the food processing industry is growing.
Such colorants are viewed as accidental colorants as they are present only
because they or their precursors are present (Mutean, 2000).

Natural pigments are generally
considered the pigments occurring in unprocessed food, as well as those that
can be formed upon heating, processing, or storage (Zdzislaw, 2002). Chlorophylls and carotenoids are the most
abundant pigments in nature. They are involved in fundamental processes and
life on earth depends on them. Chlorophyll is not found in animals but carotenoids
accumulate in some organs (e.g. eyes) and tissues e.g. skin of fish, bird
plumage (Delgaldo and Lopez, 2003). In addition, flavonoids are scarce in fungi
whereas riboflavin imparts the yellow color in the genera Russula and Lyophyllum.
Betalains, melanin, a small number of carotenoids and certain anthroquiriones
are common to fungi and plants (Delgaldo and Lopez, 2003).

More than 1000 pigments have been
identified in fungi. Fungi are not photosynthetic and do not contain
chlorophyll (Zdzislaw 2002).
Carotenoid distribution in fungi is restricted to some orders (e.g. pharagmobasidiomycetidae, and Discomycetes). All natural pigments are
unstable and participate in different reactions, so their color is strongly
dependent on conditions (Zdzislaw,
2002).

Limitations of Natural Pigment use.

Delgaldo and Lopez (2003)
reported that limitations to the use of natural pigments include; being produced
by traditional methods, having a lower intensity in comparison to synthetic
pigments and natural pigments require large quantities of raw material to
obtain the same depth level like synthetic pigments i.e. they occur in small
amounts in plants or plant part.Alsonatural pigments are highly sensitive
to pH and temperature.

Note that all
references used in all postings related to the topic of sausages, meat and meat
product colorings will be posted in the last article about this topic

About the authorMr.
Sempiri Geoffery, the author of this article graduated from
Makerere University witha Bsc In
Food Science and Technology Degree in January, 2011.

Nitrates and Nitrites are
fundamental components of the global nitrogen cycle and are therefore found throughout
the environment. Nitrates and nitrites are compounds that contain a nitrogen
atom joined to oxygen atoms, with nitrate containing three oxygen atoms and
nitrite containing two. In nature, nitrates are readily converted to nitrites and
vice versa. Both are anions or ions with a negative charge. They tend to
associate with cations, or ions with a positive charge to achieve a neutral
charge balance. (Argonne National
Laboratory, 2005).

The role of Nitrates and Nitrites in Cured Meat
Products

Potassium and
sodium salts of the nitrate and nitrites are the most extensively used of all
food additives (Stevanovic and Šentjurc, 2000). Nitrates and nitrites in cured
meat and meat products play a multipurpose role; in addition to effectively
inhibiting the growth and toxicogenic effect of Clostridium botulinum, nitrite is responsible for the development
of typical cured-meat color and flavor, and also functions as an antioxidant
(Rincón et al., 2008), retarding the development of rancidity, off-odors and
off-flavors during storage, inhibiting the development of warmed-over flavor and
preserving flavors of spices and smoke (Zdzlaslaw, 2002).

Adding nitrite
to meat is only part of the curing process (Feiner, 2006). Ordinary table salt
(sodium chloride) is added because of its effect on flavor. Sugar is added
because of its contributions to flavor, browning during frying process and its
ability to disguise high levels of salt in a meat product. Spices and other
flavorings are often added to contribute to flavor, aroma and taste but not
added for nutritional purposes (Feiner, 2006).

Sodium nitrite,
rather than sodium nitrate, is the most commonly used for curing (although in
some products, such as country ham, sodium nitrate is used because of the long
aging period) (Stevanovic and Sentjuric, 2000). In a series of normal
reactions, nitrite is converted to nitric oxide (Fennema, 1996). Nitric oxide
combines with myoglobin, the pigment responsible for the natural red color of
uncured meat forming nitric oxide myoglobin, which is a deep red color (as in
uncooked dry sausage). This changes to the characteristic bright pink normally
associated with cured and smoked meat (such as wieners and ham) when heated
during the smoking process (Feiner, 2006).

When
sodium nitrite is added with the salt, the meat develops a red, then pink
color, which is associated with cured meats such as ham, bacon, hot dogs, and
bologna. Nitrite reacts with the meat myoglobin to cause these color changes,
first converting to the unstable nitrosomyoglobin (bright red), then on heating,
to a more stable nitrosohemochrome, a pink pigment (Zdzlaslaw, 2002; Fennema,
1996).

Modification of the myoglobin
molecule takes place in the meat curing process where nitric oxide (NO), which
originates from the sodium nitrite or potassium nitrite curing agent, combines
to form nitrosomyoglobin (Fennema, 1996).

According to Feiner (2006), this
reaction takes place at pH value below 6.5 and in meat products a pH value of a
round 4.7(salami) to 6.0 is present in the final product. When used, sodium
nitrate (NaNO3) does not contribute directly to the formation of the
red curing color but rather reduced to sodium nitrite (NaNO2) thus
providing nitric oxide (NO) by the reactions above, which results into the
formation of the characteristic pink cured meat color (Feiner 2006, Fidel,
et al, 2009). Examples such products are; ham, corned
beef, bacon, salami, and sausage.

In the presence of thiol compounds
as reducing agents in the reversible reaction, myoglobin may form a green
sulfmyoglobin (Zdzlaslaw,
2002). Other reducing agents, for example ascorbate
lead to formation of cholemyoglobin making the reaction irreversible (Fiener,
2006).

Animal
blood and its dehydrated protein extracts, which are mainly hemoglobin, are a
potential source of red and brown heme pigment which may be used as red and brown
coloring to meat products. However in most countries their usage as food
colorant is not permitted (Zdzlaslaw, 2002).

Meat, nitrates, nitrites and cancerColorectal cancer is the main cancer type that has been associated with
high meat consumption. Based on a considerable number of studies a 12–17%
increased risk of colorectal cancer was associated with a daily increase of 100
g of red meat and a 49% increased risk associated with a daily increase of 25 g
of processed meat (ferguson, 2010).Processed meats include sausages, smoked beef and hams among others in
which case nitrates and nitrites are used as additives.

Hill (1991) reported that the use of nitrites in cured meats experienced
a serious drawback in the late 1960s in the usa due to the n-nitrosamines
scare. The presence of some n-nitrosamines, as a consequence of the reaction of
nitrites with secondary amines especially in thermally treated cured meats,
caused a ban in the usa that was lifted after re-considering maximum amounts to
be added. A number of n-nitrosamines are potential carcinogenic agents and are
postulated to have several deleterious health effects, so their formation must
be prevented. According to stevanivic and senjurc (2002) and hill (1991), the
addition of ascorbic acid ensured the reaction of nitrite to nitric oxide and
thus reduced the possibility for the formation of n-nitroso compounds in meat
products. N-nitroso compounds are formed by the action of nitrous acid on a
suitable secondary nitrogen group. If the parent nitrogen group is a secondary
amine, then the product is an n-nitrosamine giving rise to n-nitrosamides,
ureas to n-nitrosoureas, all of which are carcinogenic to the body. The
n-nitrosamines are target organ specific and cause tumors at sites distant from
that of their introduction into the body. N-nitrosamide and n-nitrosoureas are
locally acting and cause tumors only at their sites of introduction. The
n-nitrosamines are not directly acting mutagens but need activation by
microsomal enzymes before they are mutagenic in the salmonella mutagenesis assay. They also need to be activated in the
body, but this process which leads to the organotropism of these compounds, is
little understood (hill 1991)

In reference to the above, it is
therefore necessary to develop alternatives to nitrates and nitrites.
Researchers have proposed different methods to inhibit the possibility of
N-nitrosamine formation in cured meat products. These include a decrease in the
level of added nitrite or the use of N-nitrosamine blocking agent such as
ascorbate and α- tocopherol (Stevanivic and Senjurc, 2002). However, as far as
N-nitrosamines are concerned, the most attractive and reliable method is total
elimination of nitrites and nitrates from the curing process. The alternative
of natural plant colorants extracted directly from plants or plant parts that
totally eliminate the use of nitrite from the curing process can be a viable alternative
for coloring comminuted meat as a substitute for nitrates, nitrites and
synthetic colorants to give the products their characteristic pink color.

Note that all references used in all postings related to the topic of sausages, meat and meat product colorings will be posted in the last article about this topic.

About the authorMr.
Sempiri Geoffery, the author of this article graduated from
Makerere University witha Bsc In
Food Science and Technology Degree in January, 2011.

Sunday, 12 February 2012

The color is the
first impression consumers have of any meat product and often is their basis
for product selection or rejection (Deda et al., 2008). According to Cornforth (1998), it is
the most universal quality gauge used by consumers to judge meat
freshness.Deterioration of meat color
may indicate that the product is spoiled or has lost its nutritional
valve.Although meat color is not a good
indicator of nutritional quality, it may indicate microbial spoilage. By
maintaining meat and meat product color, we can maximize consumer quality
perception (Zdzlaslaw, 2002).

The color of meat products is
determined by a combination of different factors including moisture and fat
content, but more important is the chemical form and concentration of the
hemoproteins, especially that of myoglobin (Adamsen et al., 2006). Myoglobin (80%) and hemoglobin (20%) are
the predominant meat pigments and accounts for the red color in meat (http://labs.ansci.uiuc.edu). The color pigment of the
muscle tissue is myoglobin while haemoglobin is the color pigment of the blood
(Feiner, 2006). Myoglobin is a complex protein, similar in function to the
blood pigment hemoglobin, in that they both bind with the oxygen, which is
required for metabolic activity of an animal. Although their functions are
similar, their roles are different; hemoglobin acts as an oxygen carrier in the
bloodstream, whereas myoglobin is essentially a storage vehicle for oxygen in
muscle (Feiner, 2006).In both pigments,
the heme group is composed of the porphyrin ring system and the central iron
atom bound with the globin; in myoglobin, the protein portion has a molecular
weight of 17,000, and in hemoglobin about 67,000 (Zdzlaslaw, 2002). The color
of meat from various species, such as poultry, pork, and beef, often differs in
redness, and one cause of this difference is the amount of myoglobin in the
meat (http://meat.tamu.edu/color).

Myoglobin Structure

Myoglobin is an oxygen-binding
protein (globular protein of 153 amino acids) of the muscle (Fennema, 1996). This is the pigment chiefly
responsible for the color of meat, though hemoglobin (the oxygen-binding
protein in blood) is also present in small quantities (Feiner, 2006).
Myoglobin is a monomeric protein consists of a single-chainglobin
protein and a color giving heme group in the centre (Feiner, 2006; Fennema,
1996; Deman 1999). The heme group consists of a flat prophyrin ring exhibiting
a central iron atom (Fe2+). This iron atom has six coordination
bonds, each representing an electron pair accepted by the iron from five
nitrogen atoms; four from the porphyrin ring and one from a histidyl residue of
the globin (Fennema, 1996; Cornforth, 1998). The sixth bond is available for
binding with any atom that has an electron pair to donate, for example oxygen
and nitric oxide. The oxidation state of the iron atom and the physical state
of the globin play an important role in meat color formation (Feiner 2006; Zdzlaslaw, 2002). It has eight
alpha helices and a hydrophobic core. It has a molecular weight of 16,700 Daltons
(http://en.wikipedia.org/wiki/Myoglobin)

According to Feiner (2006) and
Cornforth (1998), myoglobin exists in three main forms, each producing a
characteristic color; purple deoxymyoglobin (Mb), red oxymyoglobin (MbO2),
and brown metmyoglobin (metMb).

In living tissue, the
physiologically active oxymyoglobin (MbO2) and deoxymyoglobin (Mb)
forms are maintained through the activity of metmyoglobin (metMb) reductase
enzymes (Feiner, 2006). These processes decline postmortem, and storage conditions become more important in
determining the proportion of each myoglobin form present (Warriss 2000).In muscle immediately after slaughter, beef meat color is a deep
purplish. As oxygen in the air comes in contact with exposed meat surfaces, it
is absorbed and combines with myoglobin, turning the meat a brighter color (Cornforth, 1998). This brighter red pigment is called oxymyoglobin. Oxymyoglobin (MbO2) is the pigment responsible for the
preferential bright red color of raw meat, and is formed rapidly in the
presence of oxygen at normal atmospheric pressure (Varnam and Sutherland,
1995). MbO2 predominates at fresh meat surface (Cornforth, 1998).

Deoxymyoglobin (dMMb) exists in
absence of oxygen, such as in the bulk of meat portions and in vacuum-packaged
meats (Fennema, 1996). The ferrous iron becomes oxidized by free radicals when
meat is stored for long periods of time, producing the brown pigment MetMb,
which also forms where oxygen-dependent meat enzymes and aerobic microorganisms
successfully compete with meat pigments for oxygen (Feiner, 2006). Myoglobin and oxymyoglobin
lose electrons (oxidize), turning the pigment brown colored called
metmyoglobin.

Fig 2; Basic transformation of
myoglobin (Zdzlaslaw, 2002)

According to Zdzlaslaw (2002),
oxymyoglobin and myoglobin exist in a state of equilibrium with oxygen; the
ratio of these pigments depending on oxygen pressure. The heme pigment in meat
is slowly oxidized to metmyoglobin and the formed metmyoglobin cannot bind
oxygen (Cornforth, 1998).

Myoglobin (only about 0.5% of the
wet weight of red meats), its response to heat largely determines the color of
cooked meat (Nicola and Rosemary 2006). Heating causes denaturation of the
globin, which then precipitates with other meat proteins. Denaturation of
myoglobin and other proteins begins between 550C and 650C
in meat, and most denaturation occurs at 750C or 800C
(Varnam and Sutherland, 1995). The rate of myoglobin denaturation decreases
with increasing meat temperature, and this is related to the simultaneous rise
in meat pH with cooking (Nicola and Rosemary 2006).

The three forms of myoglobin differ
in their sensitivity to heat. Deoxymyoglobin is the least sensitive to heat
denaturation, followed by Oxymyoglobin, then by metmyoglobin, though the latter
two (MbO2 and metMb) have fairly similar heat sensitivity. As the
globin is denatured, metMb forms the brown globin hemichromogen
(ferrihemochrome) and the other myoglobins are denatured to the red globin
hemochromogen, (ferrihemochrome) (Nicola and Rosemary, 2006). The latter is
readily oxidized to the former, so ferrihemochrome is present in larger amounts
in cooked meats (Varnam and Sutherland, 1995). Adequate cooking of meat
produces a color change to off-white, grey, or brown hues, depending on the
type of muscle (Nicola and Rosemary, 2006). The ultimate color depends on the
extent of ferrihemochrome formation, which in turn is a product of the initial
proportionality of the myoglobins, and the final concentration of undenatured
oxymyoglobin (Gorgulho, 2009). Myoglobin, oxymyoglobin, and metmyoglobin can all be changed from one
to the other when the appropriate conditions exist. (Nicola and Rosemary, 2006;
http://meat.tamu.edu/color).

A
brown pigment, which is denatured metmyoglobin, is formed with cooking, which
normally cannot be changed to form another pigment (Nicola and Rosemary, 2006).

Fig 4; Characteristics of the
myoglobin pigment in meat, their dynamic relationships, and the denatured
products formed during cooking (Source: Nicola and Rosemary, 2006).

The
Influence of pH on Cooked Meat Color

Normal fresh meat has a pH ranging
from 5.4 to 5.6 (Varnam and Sutherland, 1995). The amount of ferrihemochrome
formation from myoglobin during cooking is affected by initial meat pH
(Gorgulho, 2009). The muscle contains glycogen but with postmortem, glycogen is
broken down to lactic acid, lowering the pH due to a reduction in oxygen supply.
This acidification process continues until either the glycogen is consumed or
the low pH inactivates glycolytic enzymes (Varnam and Sutherland, 1995).

Meat with a pH above 6.2 tends to
have a tightly packed water-retaining fiber structure that impedes oxygen
transfer and promote longer survival of oxygen-scavenging enzymes, favoring Mb
rather than MbO2 (Varnam and Sutherland, 1995). The purple-red
myoglobin combines with the closed structure of the muscle to absorb rather
than reflect light, making the meat dark, firm and dry (DFD) and for the pale,
soft, exudative (PSE) meats, postmortem
glycogen levels are reasonably high, and the acidification is accelerated so
that the pH falls rapidly, while the muscle is still warm (Feiner, 2006; Adams
and moss, 2000). The combination of high temperature and low pH causes protein
denaturation, water loss and an open muscle structure. The low pH also tends to
promote oxidation of MbO2 and Mb to brown metMb, which combines with
high light scattering from the meat surface, giving the meat its pale color
(Adams and Moss, 2000).

The extent to which pH affects the
cooked color of meat varies between species (high pH lowers myoglobin
denaturation and meat becomes more red) (Nicola and Rosemary, 2006). Meat pH
also influences other factors that affect cooked meat color. According to
Nicola and Rosemary (2006), these factors include; fat content, freezing and
rate of thawing, the initial form of the myoglobin (for example, Mb is less
heat-sensitive and more stable at higher pH than other myoglobin forms), the
condition and structure of the muscle fibers (for example, DFD vs. PSE), and
the denaturation processes of other meat proteins, including enzymes.

Note that all references used in all postings related to the topic of sausages, meat and meat product colorings will be posted in the last article about this topic.

About the authorMr. Sempiri Geoffery, the author
of this article graduated
from Makerere University witha Bsc In Food Science and Technology Degree in January, 2011.

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